Light-emitting diode (LED) devices have been actively developed since Nakamura and the like of Nichia Corporation of Japan succeeded in fusing a high-quality monocrystalline GaN nitride semiconductor in 1992 by applying a low-temperature GaN compound buffer layer thereto. An LED is a semiconductor having a structure in which an N-type semiconductor crystal in which a plurality of carriers are electrons and a P-type semiconductor crystal in which a plurality of carriers are holes are bonded to each other by using a characteristic of a compound semiconductor, and is a semiconductor device which converts an electrical signal into light having a wavelength band of a desired region to display the light. In Korea Unexamined Patent Application Publication No. 2009-0121743, a method of manufacturing an LED and an LED manufactured thereby are disclosed.
The LED is a green component which has very low energy consumption due to high light conversion efficiency, has a semi-permanent lifetime, and is environmentally friendly. LEDs are being applied in many fields such as traffic lights, mobile phones, automobile headlights, outdoor electric signboards, liquid-crystal display (LCD) backlight units (BLUs), indoor/outdoor lights, and the like, and are being actively researched domestically and internationally.
As part of the above research, research on an ultra-small LED device which is manufactured to have a nano size or a micro size is actively being conducted, and research for utilizing such an ultra-small LED device in lighting, a display, and the like is being continued. In such research, an electrode for applying power to an ultra-small LED device, an electrode arrangement for reducing a space occupied by the electrode and an application purpose, a method of mounting an ultra-small LED on an arranged electrode, and the like are continuously being focused on.
Among the above things, the method of mounting an ultra-small LED on an arranged electrode still has difficulty in that it is very difficult to arrange and mount an ultra-small LED device on a target electrode due to a size limitation of the ultra-small LED device. This is because the ultra-small LED device is on a nano-scale or micro-scale and may not be arranged and mounted in a target electrode region by a human hand.
Also, even when the ultra-small LED device is mounted in the target electrode region, it is very difficult to adjust the number of ultra-small LED devices included in a unit electrode region and a positional relationship between ultra-small LED devices and electrodes as desired. When LED devices are arranged on a two-dimensional plane, the number of LED devices included in a unit area is limited and it is difficult to obtain an excellent amount of light. Furthermore, because all ultra-small LED devices connected to two different electrodes cannot emit light without a defect such as an electrical short-circuit and the like, it is more difficult to obtain a desired amount of light.
Accordingly, the inventor of the present invention has proposed a method of manufacturing a nano-scaled ultra-small LED device which is implemented as an electrode assembly by applying power to the ultra-small electrode line in Korean Patent Registration No. 10-1490758 to implement an ultra-small LED electrode assembly. However, in the ultra-small LED electrode assembly implemented by such a technique, the number of ultra-small LED devices which do not emit light when a DC is applied thereto as driving power is significantly increased, and thus it is difficult to obtain a desired luminance. In order to address the above problem, there is a selection limitation of power to which an alternating current (AC) should be applied as the driving power. Such results are due to characteristics of the LED itself as a rectifier. A direction of a current in a device may be determined by a structure of layers in the device. For example, in the case of an LED in which a P-type semiconductor and an N-type semiconductor are bonded to each other, when positive (+) power is connected to the P-type semiconductor and negative (−) power is connected to the N-type semiconductor, a current may flow through the LED due to a potential difference generated while free electrons of the N-type semiconductor move toward positive holes of the P-type semiconductor, and the LED may emit light while the free electrons recombine with the positive holes. However, since no current flows in the LED when the negative (−) power is connected to the P-type semiconductor and the positive (+) power is connected to the N-type semiconductor, an ultra-small LED electrode assembly implemented to have no semiconductor directionality of ultra-small LED devices and no disposition tendency between different mounting electrodes has a problem in that some of the ultra-small LED devices may not emit light when DC driving power is applied thereto and a luminance thereof is significantly reduced.
Accordingly, research on an ultra-small LED electrode assembly in which ultra-small LED devices communicate without an electrical short-circuit, a selection limitation of driving power is removed, and a luminance thereof is further improved is urgently required.